1. Field of the Invention
The present invention relates to a magnetic recording medium comprising a base film coated with an intimate mixture of magnetic powders in a binder, that is, to a magnetic recording tape suitable for sound or video recording or for use in electronic computers. More particularly, the invention relates to a magnetic recording medium which is free of "squeal" phenomenon when running as a magnetic recording tape and which provides smooth and stable running performances especially in an environment of high temperature and high humidity.
2. Description of the Prior Art
In general, when used with recording-reproducing devices such as a cassette tape deck, a magnetic recording tape runs in contact with magnetic heads, tape guides, pinch roller, capstan, etc. Therefore, the magnetic recording tape is required to possess a low friction coefficient as well as smooth and stable running performances. However, when the magnetic recording tape is running, a continuous phenomenon of stick-slip occurring alternately at the contacting portion of the magnetic coating layer with the magnetic heads or tape guides is sometimes observed. When this alternate stick-slip motion gradually intensifies, longitudinal vibrations of the tape will occur. These longitudinal vibrations are known as "stick-slip vibration" and are primarily responsible for the "squeal" phenomenon of the magnetic tape. Recently, this "squeal" phenomenon readily occurs because of the trend toward dense magnetic recording and magnetic tapes such as audio cassette tapes are designed for low running speed (4.75 cm/sec.) and frequency in use of thinner tapes (thickness 6 to 18 .mu.m) has become high.
In order to ensure stable running properties of these magnetic tapes, it has been conventional practice to incorporate into the magnetic coating material, besides a binder, any of various lubricants such as higher fatty acids or their derivatives, liquid paraffin, castor oil, fluorine oil, molybdenum disulfide, powdered graphite, etc. However, none of these lubricants can provide adequate lubricity to the magnetic tape. Particularly, they are unsatisfactory for ensuring stable running performance and preventing the squeal phenomenon of the tape in an environment of high temperature and high humidity (for example, a temperature of 40.degree. to 60.degree. C. and a relative humidity of 70 to 80%). The present invention has as its object the provision of a magnetic recording medium which obviates the above mentioned drawbacks of the prior art.